Scan Sequenced Power-On Initialization

ABSTRACT

A scan sequenced initialization technique supplies a predefined power-on state to a device or module without using explicit reset input to the registers. This invention supplies a predefined pattern to parallel scan chains following power-on reset. These parallel scan chains are already required for structural manufacturing test. Once the power-on reset scanning is complete, the power-on reset sequencer indicates completion of state initialization to other circuits. These other circuits are those which interact with the module or device using this invention.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(e)(1) to U.S. Provisional Application Nos. 60/680,635 and 60/681,427 both filed May 13, 2006.

TECHNICAL FIELD OF THE INVENTION

The technical field of this invention is initialization of integrated circuit electronics.

BACKGROUND OF THE INVENTION

A guaranteed power-on initialization state in complex SOC designs is essential to ensure proper silicon functionality. This also enables robust functional manufacturing test patterns. This can be difficult and expensive to achieve for large designs, if a reset of each state element is performed. Such a technique tends to crate design process inefficiency associated with gate-level netlist bring-up by requiring much time to be spent with initialization issues.

SUMMARY OF THE INVENTION

A scan sequenced initialization technique supplies a predefined power-on state to a device or module without using explicit reset input to the registers. This invention supplies a predefined pattern to parallel scan chains following power-on reset. These parallel scan chains are already required for structural manufacturing test. Once the power-on reset scanning is complete, the power-on reset sequencer indicates completion of state initialization to other circuits. These other circuits are those which interact with the module or device using this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in the drawings, in which:

FIG. 1 illustrates the circuits of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 illustrates a conceptual block level diagram of system 100 of this invention. System-on-chip module 110 includes plural scan chains 111, 112, 113, 114 and 115 for manufacturing test. In this example each of these scan chains 111, 112, 113, 114 and 115 includes 256-bit chains. These scan chains 111, 112, 113, 114 and 115 are fed by either the test control logic 120 or power-on sequencer 130.

Upon initial application of electrical power or upon a predetermined signal on the power-on-reset (POR) pin, power-on sequence control 130 supplies a power-on scan enable signal to test control logic 120. Test control logic 120 responds by supplying a scan enable signal to scan chains 111, 112, 113, 114 and 115. As known in the art, the scan enable signal changes SOC module 110 from an operational mode to a scan-in mode. In the scan-in mode various register bits of SOC module 110 are connected into one or more serial scan chains. The example of FIG. 1 includes five such scan chains 111, 112, 113, 114 and 115. Also as known in the art, application of a scan clock controlled by test logic control 120 causes data to shift along each scan chain 111, 112, 113, 114 and 115 from an input to an output.

In response to the power-on scan enable signal, test logic 120 does not supply inputs to scan chains 111, 112, 113, 114 and 115. Instead test logic 120 controls multiplexers 141, 142, 143, 144 and 145 to select signals from power-on sequence control 130. Power-on sequence control 130 supplies predetermined input patterns to the scan chains 111, 112, 113, 114 and 115 via the corresponding multiplexers 141, 142, 143, 144 and 145. The pattern applied to the module can be an architecturally specified reset state or a safe power-on state, such as all zeros. These patterns may be read from a read only memory 135 into the scan chains. Alternatively, these scan patterns may be generated by any suitable scan generator.

Power-on reset sequence control 130 operates for a number of scan clock cycles to completely fill the longest of the scan chains 111, 112, 113, 114 and 115. In the example of FIG. 1 the longest scan chain is 256 bits. Thus each scan chain 111, 112, 113, 114 and 115 is fed a pattern of 256 bits. Following completion of 256 scan clock cycles, which may be measured by a counter 137 within power-on sequence control 130, power-on sequence control 130 stops generation of the power-on scan enable signal. Test control logic 120 responds by no longer generating the scan enable signal. Scan-in of data via scan chains 111, 112, 113, 114 and 115 then stops. Test control logic 120 then controls multiplexers 141, 142, 143 and 145 to select pattern data from test control logic 120 rather than from power-on sequence control 130. Also upon time out of the scan chain length, power-on sequence control 130 generates a power-on reset (POR) initialization done signal on external pin 102. This enables devices external to system 100 to determine when power-on initialization is complete. Note following power-on initialization, test control logic 120 operates according to the known art to permit manufacturing test by scanning in one or more states for test.

Those skilled in the art would recognize that multiplexers 141, 142, 143, 144 and 145 could be replaced by wired ORs. When power-on sequence control 130 supplies initialization input pattern(s), test logic control 120 supplies zeros. Thus only the initialization input pattern is supplied to the corresponding scan input. Similarly power-on sequence control 130 would supply zeros when test logic control 120 supplies test pattern(s). This reduces the complexity of multiplexers 141, 142, 143, 144 and 145 at the expense of requiring zero outputs from test logic control 120 and power-on sequence control 130 when not selected.

This invention does not rely on explicit reset terms on register elements to force a power-on reset value. Instead uses a serial scan technique to apply the values. This invention uses hardware which would already be present in SOC designs. Therefore the overhead in guaranteeing the important initialization state using this invention is cheap and reliable. This invention offers some relief to timing overhead associated with reset on the register to register paths. With SOCs having increasing clock speeds this enables fast initialization without timing overhead. This invention also reduces the overhead on power and area associated with dedicated reset terms to support equivalent means of power-on initialization. 

1. A method of initialization of an integrated circuit including a scan chain with a scan chain input comprising the steps of: upon initialization of the integrated circuit enabling scan chain input; supplying a predetermined initialization input pattern to the scan chain input; shifting said initialization input pattern into said scan chain for a predetermined number of scan clock cycles; and disabling scan chain input.
 2. The method of claim 1, wherein: said initialization input pattern represents a predetermined initialization state for said integrated circuit.
 3. The method of claim 1, wherein: said initialization input pattern is all zeros.
 4. The method of claim 1, further comprising the step of: storing said initialization input pattern in a real only memory.
 5. The method of claim 1, wherein: said initialization input pattern has a length equal to a length of said scan chain.
 6. The method of claim 1, further comprising the step of: signaling initialization reset done after said predetermined number of scan clock cycles.
 7. The method of claim 1, further comprising the step of: supplying a predetermined test input pattern to the scan chain input at a test time different from said initialization.
 8. The method of claim 1, wherein the integrated circuit includes a plurality of scan chains each having a scan chain input and wherein: said step of supplying a predetermined initialization input pattern to the scan chain input comprising supplying corresponding initialization input patterns to each scan chain input; and each of said initialization input patterns has a length equal to a length of a longest of the plurality of scan chains.
 9. An integrated circuit comprising: a scan chain with a scan chain input; a power-on sequence control circuit operable upon initialization of the integrated circuit to enable scan chain input, supply a predetermined initialization input pattern to the scan chain input, shift said initialization input pattern into said scan chain for a predetermined number of scan clock cycles, and disable scan chain input.
 10. The integrated circuit of claim 9, wherein: said initialization input pattern supplied by said power-on sequence control circuit represents a predetermined initialization state for said integrated circuit.
 11. The integrated circuit of claim 9, wherein: said initialization input pattern supplied by said power-on sequence control circuit is all zeros.
 12. The integrated circuit of claim 9, further comprising: a real only memory storing said initialization input pattern.
 13. The integrated circuit of claim 9, wherein: said power-on sequence control circuit is further operable to supply aid initialization input pattern in a length equal to a length of said scan chain.
 14. The integrated circuit of claim 9, wherein: said power-on sequence control circuit is further operable to signal initialization reset done after said predetermined number of scan clock cycles on an integrated circuit pin.
 15. The integrated circuit of claim 9, wherein: said power-on sequence control circuit is further operable to supply a power-on scan enable signal upon initialization of the integrated circuit; said integrated circuit further comprising: a test logic control circuit connected to said power-on sequence control circuit operable to supply a predetermined test input pattern to the scan chain input at a test time different from said initialization; and a multiplexer having a first input receiving said initialization pattern input, a second input receiving said test pattern input, an output connected to said scan chain input and a control input controlling connection of one of said initialization pattern input or said test pattern input to said multiplexer output; wherein said test logic control is operable to supply a scan enable signal to said scan chain upon receipt of said power-on scan enable signal, supply a control signal to said control input of said multiplexer upon receipt of said power-on scan enable signal to select said initialization pattern input, end said scan enable signal to said scan chain upon end of said power-on scan enable signal, and supply a control signal to said control input of said multiplexer upon end of said power-on scan enable signal to select said test pattern input.
 16. The integrated circuit of claim 9, wherein: said scan chain comprises a plurality of scan chains each having a scan chain input; and said power-on sequence control circuit is further operable to supply a corresponding initialization input patterns to each scan chain input; and each of said initialization input patterns has a length equal to a length of a longest of the plurality of scan chains. 